1. Technical Field
The present invention relates generally to structures having sub-microscopic holes and more particularly to structures having nano-size pores.
2. Background Art
In many fields, especially biology and electronics, it has become important to be able to form smaller and smaller openings or pores in order to be able to advance the technology.
For example in biology, it has become important to be able to study single-stranded DNA and RNA in various fields, such as medicine and biological research. By studying DNA and RNA, various diseases can be detected and treated.
Unfortunately, the individual components of the DNA and RNA are nano-scale structures (10−9 meter and below), which are sub-microscopic and cannot be read directly. For example, a single-stranded DNA is made up of a number of components called “nucleotides”, which are designated by the letters A, C, G, and T (for adenine, cytosine, guanine, and thymine). The human genome is about 3.2 billion nucleotides long, which is analogous to a million-page book having different length words and 3,200 letters per page.
In order to be able to read a single-stranded DNA or RNA, it is necessary to be able to process one strand at a time. Unfortunately, there is currently no method that allows a direct measurement of one strand or even a method to line up the single strands in such a way that they may be read.
The ideal would be to electronically sense biological polymers, like RNA, DNA, and proteins, and also unlabeled polynucleotides at a molecular level so as to be able to characterize individual molecules with regard to length, type, and sequence. This would be accomplished by passing a strand of molecules through an opening or pore in a membrane and electronically sensing the molecules. In addition to a problem forming the electrodes for the electronic sensing, the major problem has been with making an opening or pore small enough that only one strand of molecules would pass through.
Methods used in the past for creating the required opening or pore included both organic and inorganic techniques. For example, a lipid bilayer membrane would be forced across a 30-μ hole in a piece of PTFE separating two compartments filled with buffer fluids. A chemical, (α-hemolysin, would be added to one of the buffer-filled compartments and the α-hemolysin would attack the lipid bilayer membrane for five minutes. Generally, a 2.6 nm diameter ion channel would form, after which the α-hemolysin was immediately flushed out to prevent other pores from forming. However, there was no easy process of crosschecking that there was indeed only one pore and there was also an inability to place a single pore in a particular location.
Another approach used an organic pore synthesis using a freestanding silicon nitride film. The film is sputtered using a focused ion beam (FIB) with a feedback system that stops the FIB once ions are detected on the other side of the film. The process was then continued by redepositing silicon nitride in an effort to close up the opening to a desired size. This has also been problematic due to the difficulty of controlling the nitride deposition.
None of the prior art approaches were able to produce openings of a known size at a known location or assure only that a single pore was being manufactured. Further, the processes were not predictable and were time-consuming for forming single pores when successful.
A solution to this problem has been long sought, but has long eluded those skilled in the art.